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The effects of disturbance on the emergence of eurasian badgers in winter
Biological Conservation 34 (1985) 289-306
The Effects of Disturbance on the Emergence of Eurasian Badgers in Winter
I. M. Lindsay & D. W. Macdonald Department of Zoology, South Parks Road, Oxford OXI 3PS, Great Britain
ABSTRACT Eurasian badgers are widespread on English farmland where they may be affected by various human activities, amongst which is the practice of 'earthstopping' by foxhunts. This practice is described in detail, and involves blocking the entrances to badger setts in order to prevent the escape therein of hunted foxes. A questionnaire survey indicates that earthstopping is practised on 30.8 % of English fiTrms and that in some areas most badger setts are routinely stopped 4-5 times during the winter foxhunting season. Setts were monitored and badgers radio-tracked in an investigation of the consequences of stopping for their behaviour. The time of nightly emergence from the sett was found to be negatively correlated with minimum nightly temperature, and badgers rarely emerged at all on nights when the temperature fell to - 1 °C or below. When subjected to stopping the badgers postponed their emergence times and did not emerge at all on some nights when, on the basis of the temperature, they would otherwise have been expected to do so. However, we could detect no damaging effect upon the badgers due to these delays or otherwise due to stopping when it was practised responsibly. In contrast, irresponsible stopping with rubble rather than loose soil is pointless, damaging to the landscape andprobably also to the badgers. We conclude that where stopping is deemed necessary it should only be done either with loose soil, which the badgers can readily dislodge, or with bungs such as soil-filled sacks, which the huntsmen should remove at the end of the day's hunting. 289 Biol. Conserv. 0006-3207/85/$03.30 ~/Elsevier Applied Science Publishers Ltd. England 1985. Printed in Great Britain
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I N T R O D U C T I ON The Eurasian badger, Meles meles, is a 10kg nocturnal mustelid (subfamily Melinae) which lives in territorial groups of 2-12 members, that occupy a communal den or sett (Neal, 1977a: Kruuk, 1978). In addition to the 'main sett7 which is often located centrally in the territory, there are other holes, termed 'outliers', which some badgers may use intermittently. Main setts comprise several entrances (generally 6-10 but 100 have been recorded, Neal, 1977a) and are in traditional sites which may have been used continuously for centuries. In mid-winter, badgers remain largely in the sett. This period of inactivity may last, in Great Britain, from December to March. Eurasian badgers in Britain are widespread on farmland (Neal, 1977b) where they are tolerated, and even welcomed, by most farmers, to whom they generally cause minimal damage (Macdonald, 1984). On about 80 ~/oof English farmland red foxes Vulpes vulpes are hunted with hounds and mounted followers. When pursued, foxes may seek sanctuary underground, including badgers' setts, in which they often shelter by day even when undisturbed. Therefore, burrows in general, and badger setts in particular, are seen as an impediment to fox hunting for two reasons: first, a hunted fox taking refuge in a burrow may thereby escape completely, or necessitate laborious and protracted digging-out. Either outcome diminishes the opportunities for challenging horsemanship for the assembled 'field'. Second, loxes which have taken refuge in holes before the hunt arrives are from the outset much less accessible. In an attempt to avert these problems, fox hunters block burrow entrances into which foxes might flee or lie-up--a practice known as ~earthstopping'. During the foxhunting season (September to March) the entrances to badger setts are ~stopped' on hunting days throughout much of rural England. Setts are also sometimes stopped by farmers or others who are not necessarily concerned with hunting. The practice of stopping setts is controversial in that it might have damaging consequences for the badgers. In the hope of diminishing any such consequences the fox hunters" governing body (Masters of Foxhounds Association, MFHA) issues guidelines for earthstoppers; they recommend that sett entrances may be blocked with loose balls of wire mesh which can easily be removed by hunt servants and which allow the passage of air. Alternatively, they suggest that sacks filled with soil can be used as temporary bungs to be removed at the end of the day (e.g. in the
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pamphlet Predator), mammals in Britain, Council for Nature, 1977). However, there are no data on the consequences tbr badgers of stopping, or how closely the guidelines are followed. Various potentially deleterious effects of stopping have been mooted, including prevention or delay of emergence, stress-induced reproductive failure and desertion of the sett, suffocation, and unsustainable expenditure of energy to unblock holes at a time when food is scarce. Within the context of a wider study of the ecology of badgers on farmland in the English Midlands we have sought to quantify the types of disturbance to which they are subjected. Disturbance due to agricultural activities appears generally to be infrequent and tolerable, and is summarised elsewhere (Macdonald, 1984). In this paper we will describe and quantify earthstopping on farmland and some of its consequences. In particular, by studying its effects on their emergence times, we will try to answer the question of whether earthstopping is detrimental to badgers. A change due to earthstopping in the time of emergence from the sett has the merit of being an immediate and readily quantifiable measure of disturbance. In selecting this measure we recognised that it does not reveal some of the possible long-term consequences, for example, changes in reproductive success, but measurement of these were beyond the scope of our study. We have, however, monitored sett utilisation throughout the study, in order to assess whether stopping was associated with any change in the pattern of occupation.
METHODS
Frequency and distribution of stopping Two questionnaires were sent to farmers, each enquiring about diverse aspects of wildlife on their farms. Respondents to the first questionnaire (Sample A, 1979 80) numbered 867 and came from 10 regions of England, whereas the 101 respondents to the second questionnaire (Sample B, 1982) came from Buckinghamshire, Oxfordshire and Warwickshire. Farmers in Sample A were asked 'How many badger setts do you know of on your land ?' and "Are fox and badger holes stopped on hunting days?'. Farmers in Sample B were also asked about numbers of setts on their land and, specifically, whether badger setts were stopped on hunting days. In enquiring about badger setts we told farmers that 'Setts
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can be recognised as a clump of 2 or more entrance holes (each about 10" diameter) with large spoil heaps of soil. Setts are normally occupied for many years. Individual badgers may occasionally live in single holes 100 yds or more from the main sett, but we do not count these "outliers" as "main setts". Please confine your answers to main setts'. We were aware of the difficulties of defining main setts and of relating numbers of setts to numbers of social groups, but felt that these guidelines were easy to comprehend and adequate to define most main setts (cf descriptions in Neal, 1977a).
Stopping of badger setts and re-opening Our field study area, like most of rural England, fell within the 'country' (territory) of one pack of foxhounds. By daily visits to a sample of main setts we recorded the incidence and details of stopping. After a day of fox hunting we then monitored the badgers' activities in re-opening blocked entrances over subsequent days.
Factors affecting emergence In our study area, 30km 2 around the village of Waddesdon, Buckinghamshire, badgers were equipped with 102 KHz radio transmitters fitted to leather collars. The transmitters followed the two-stage circuitry designed by Macdonald & Amlaner (1980) and were equipped with a motion-sensitive mercury switch. Signals were received on a Telemetry Systems Inc. (Minneapolis, USA), receiver, via either a threeelement Yagi antenna mounted on a car or via a collapsible dipole antenna, used on foot (for construction details see Amlaner, 1980). Observations at setts confirmed that a combination of changes in signal strength and activity (indicated by the motion-sensitive switch) heralded the emergence of a radio-tagged badger from its sett. In this study of the consequences of 'stopping' we were concerned with emergence in winter, when badgers sometimes leave the sett only late at night or not at all (Neal, 1977a). Observation at setts was thus hopelessly unrewarding and so we utilised an automatic timing box and recorder to monitor the radiosignals all night. The apparatus is described in Macdonald & Almaner (1980). The timing box scanned the required radio-frequencies and recorded the signal from each for 10 s every 5 rain. Listening to the tape we
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scored the volume of the signal on a subjective scale of increasing volume (1-5) and whether the mercury switch indicated movement. Comparing these 10 s transcriptions with the signal characteristics of badgers under observation, we decided the times at which badgers emerged from or returned to their setts. For some individuals we also scored the times at which they first became active each night and the first burst of protracted activity, as indicated by three consecutive active scans (i.e. spanning 10min). Times will be given in hours and decimal minutes. Where calculations involve nights on which a badger failed to emerge at all these are scored as emergence at 06.00 h in the morning (all such calculations use a 24h clock running from midday, so that 06.00 h is taken as 18.00 h during the calculation). In general, emergence from the sett was quite easily recognised by increased activity together with a change from a muffled to a sharp signal tone and a marked increase in signal volume. Sometimes, however, interpretation was ambiguous. For example, a similar record could result from a badger either poking its head from a hole and then retreating underground, and from another which emerged and then rapidly left the area. Of our various measures, duration of emergence was most susceptible to this type of ambiguity, but time of first emergence from the sett was generally clearcut. Ambiguity of this type was minimal largely because the badgers rarely left the vicinity (c. 50-100m) of the sett when they emerged. Transcriptions were least confusing the more continuous the night's record;we found that the 5 min interval and 10 s scan was the best compromise, minimising ambiguity and redundancy, while neither exceeding the capacity of the tape spool nor generating an insurmountable task in transcription. It will be shown that badgers differ individually in their emergence behaviour. Therefore, we have compared the activity of the same individuals when they are, or are not, subjected to stopping, while taking into account other possible relevant factors. Individual badgers will be referred to by the two letter code of their sett and a third letter (M or F) denoting their sex; thus CBF is a sow from sett CB. In one case the radiocollared badger SS(A)F lived in an annex about 100 m from the main sett. On each night when a badger's activity was monitored, the weather conditions were also noted and a record taken of the night's minimum ground temperature, using a maximum and minimum thermometer. The incidence of stopping was monitored at setts where badgers were radiocollared. At these setts all entrances were stopped, using soil, and none was reopened by people.
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RESULTS
Frequency and disturbance Of the 867 farmers who responded in Sample A, 604 answered the question of whether or not holes (badger or other) on their land were stopped on hunting days. 30.8 ~ replied that fox and badger holes were stopped on their land. Their answers are presented regionally in Table 1. The regional differences in frequency of stopping do not correlate with the number of setts reported per km sq estimated from the same farmers' reports on the number of badger setts on their land (r = - 0 . 2 , df. 8; ns). Table 1 also shows the regional variation in the percentage of farmers who at least occasionally follow foxhounds, and this figure does correlate weakly with the frequency of stopping (r = 0.57, df. 8; p < 0.1 > 0.05). The answers from respondents in Sample B gave a similar impression; 45 of the 101 farms reported the presence of main setts, and on 29 (64.4 ~o) of these the setts were stopped on hunting days (modally 4-5 times per season). Overall, foxes were hunted with hounds on 82.2 ~ of these 101 farms, and open holes (badger or other) were stopped on hunting days on 29 ~ . The only farmers who reported stopping on their land were those who reported badger setts, suggesting that hunt servants concentrate their stopping activities on badger, rather than fox, holes. Extrapolating from these figures one can see that earthstopping affects a large number of badgers. For example, in the English Midlands, from which our sample farms were drawn, farmers reported a mean of 0.5 setts per km 2 of farmland, equivalent to one sett stopped per 3.1 km 2 of farmland. In fact, in the 700 km 2 covered by the foxhunt in our study area, figures provided by hunt servants suggested that roughly 200 setts were routinely stopped during the foxhunting season.
Stopping and re-opening In summer, the 27 setts in our core study area had an average of 9.8 unobstructed entrances (SD 4.5), with most (53-6~) having 6-10 entrances. An earthstopper arriving at a sett attempts to find and block every entrance. The prevalent method of stopping with soil simply involved shovelling soil into the entrance and stamping it firmly into place. Holes that had been stopped are often recognisable by angular rather than circular entrances due to old spade cuts. In our area neither
TABLE 1
o~ 'Stopping' /o N Badger setts (km -2) ~o Foxhunters
30.8 604 1-2 33.9
28,3 99 0.5 30.4
Overall Ox/Bucks 21-0 62 1.1 30-5
Warks 57.9 107 2.5 40.5
Dorset 39.7 31 0.3 22,4
Salop 40"9 44 0.3 38"0
Leics 15-5 77 0-2 38.2
Yorks
5'0 20 2.3 22.5
12.5 24 0.1 18.4
Cornwall Suffolk
45-6 57 1'4 62.8
Exmoor
8"9 67 2.5 26-8
Sussex
The Overall and Regional Percentage of Farmers in Sample A Who Reported that Either Badger or Fox Holes were Stopped on Their Land on Stopping Days, Together with the Density of Badger Setts per km sq and the Percentage of Farmers who Stated that they at Least Occasionally Engaged in Foxhunting (The density of badger setts was calculated from each farmer's estimate of the number oflsetts on his land and the farm's area. The numbers of farmers answering each question on the questionnaire varied slightly and the sample sizes given here (N) refer to those answering the question on stopping, which represents 69.7 ~ of the total sample of respondents. The estimates of sett density and the percentage of hunting farmers are based on the answers of 676 and 853 respondents, respectively.)
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I . M . Lindsay, D. W. Macdonald
plugs of wire nor of soil-filled sacks were used. Sometimes empty fertiliser bags, logs, metal drums and other rubble or debris were used in an attempt to block entrances permanently, when they might also be stuffed with diesel-soaked rags. Pock-marks in the ground around setts may indicate that some holes are never re-opened. We visited 30 setts during the days following their being stopped for hunting. Only 80 ~ of the entrances had, on average, been re-opened after two weeks. During the first night between 10-100 ~o of stopped holes are unblocked by badgers (holes re-opened by rabbits, and hence with a diameter too narrow for badgers to pass, were excluded). On average the badgers opened 2.4 (SD + 1.4, n = 39) holes on the first night after stopping, and a steadily increasing percentage of holes had been re-opened as days passed (r = 0.37, df 166, p < 0.001). Some holes might remain blocked for three weeks or more, and the rate of re-opening was affected by the total number of entrances at the sett. Thus, at small ( < 4 entrances) setts a mean of 1.2 (SD + 0.4, n = 11) holes were re-opened on the first night, while at larger ones (> 4 entrances) this mean was 2.9 (SD + 1.3, n = 26). A multiple regression of percentage of entrances re-opened against days (up to 21) since stopping and number of sett entrances gave a multiple regression coefficient of 0.55 (df 166, p < 0.001) with the two independent variables accounting for 13 ~ and 18 ~o of the variance respectively. A partial correlation analysis controlling for sett size alone (r = 0.4, df 165, p <0.001) is not improved by additionally controlling for month (advancing from September to February). In summary, up to six holes might be re-opened on the first night, a greater percentage remaining unopened at larger setts on subsequent days. This pattern is shown in Fig. 1, which presents the mean percentages of re-opened holes, for setts of different sizes, on successive days after stopping. The slopes for regressions through these means intersect with the first night at 51.1 ~ , 41.2 ~ and 17.2 ~o of holes re-opened at small, medium and large setts respectively. A comparison of the number of open entrances seen at each sett at the beginning and the end of the hunting season for 16 setts which were stopped showed a decline during each of two years; in 1978 to 1979 the mean number of open entrances fell from 8.4 to 6.6 (a mean percentage change of - 2 9 . 4 ~) during the hunting season, whereas in 1979-80 it fell from 7.2 to 6.4 (a mean percentage change of - 10-I ~o), by 10.1 ~ , for the same setts. During 1978-79 three setts maintained their initial complement of entrances by the end of the season, while in 1979-80 eight
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DAYS SINCE STOPPING Fig. 1. The mean percentages of entrances re-opened by badgers on successive days following stopping, for setts with 2 entrances (O), 3-12 entrances (O) and 13 or more entrances (11). Regression lines are drawn through each set of means. did so. Therefore, in the second season fewer setts showed a decline and of these which did so the decline was smaller. There was no difference in the frequency of stopping between the two years. Despite the intention of blocking all entrances to a sett, we found that of 48 occasions, when we visited supposedly stopped setts on hunting days, on only 20 (41.6 ~o) occasions were all the holes completely stopped. Sometimes considerable effort had been expended on blocking holes with heavy boughs while other entrances were left completely open. If all setts had been completely stopped then all points would fall on the diagonal line drawn on Fig. 2. At least some of the entrances were blocked with logs at six of 18 setts where details of the stopping methods were recorded. In our core study area we visited 20 setts on each hunting day over three seasons. In that time 5 (25 ~o) were never stopped, 5 were stopped thoroughly everytime and 10 (50 ~o) were at most incompletely stopped. Of the latter 10, an average of just under one hole (0-9 SD + 0.68)was left open accidentally on each hunting day.
Emergence studies Over three years the emergence activities of seven radio-collared badgers from 5 setts were monitored using the automatic timing box. The results
I . M . Lindsay, D. W. Macdonald
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for 1979-80 are presented separately from those for 1980-81 and 1981-82, since in the first season data on temperature were measured at a nearby airforce base, and not at the setts themselves. One badger, WPM, studied in January and February 1980, only emerged twice in 21 nights and therefore could not be used in the following analyses. All six of the remaining badgers yield a negative slope relating time of first emergence to minimum nightly grass temperature, and for five of them this relationship was significant at p < 0.01. Despite this overall relationship, the badgers differed in their behaviour, as detailed below. Between January and March 1980 time of first emergence was recorded for W P F on 22 nights, including 9 when the sett had been stopped. On the latter 9 nights the mean emergence time of the badger was 00.70h, whereas on the remaining 13 undisturbed nights it was 21.50 h. Overall, therefore, a delay of 3.2 h (3 h 12 min) was associated with stopping, but as shown on Table 2, this delay was influenced also by temperature; On warm nights (min > 5.0 °C) the mean delay was 1 h 14 min. The only night on which the badger did not emerge at all followed stopping, when the minimum temperature was rather high at 2.0°C. Two males from the same sett, WIM! and WIM2, monitored for 14 nights during November and December 1979, both emerged later, on average, than W P F (t _< 5.3, df 25, p < 0.001). Although both these males had the same mean
299
Effects of disturbance on badgers
TABLE 2 Variation in the Mean Time of First Emergence from the Sett of One Badger (WPF) from January to March 1980, Contrasting Nights when Setts Had, or Had Not, Been Stopped During the Previous Day (The badger emerged later following stopping and this delay is shown for cold, mild and warm nights (nightly mean temperatures measured at a nearby meteorological station). Time is expressed as hour (on a 24 h clock) and decimalised minutes.) Min. temp. °C
>5.0 <5.0>2.0 <2.0
No stopping
Stopping
Mean Mean Ist rain. °C emergence
n
6.5 3.6 -0.7
7 5 3
20.6 22.2 22.4
Delay
Mean Mean Ist rain °C emergence
5.0 3.7 1.3
21.8 1.7 2.6
3 3 3
1.2 3.5 4.2
emergence time on those nights when they did emerge (23.00h versus 23.43 h), WIM2 emerged significantly later on colder nights (r = - 0 . 7 2 , df 12; p < 0-01) whereas WIM1 did not (r = - 0 . 3 , df 11 ; ns). Thus there was no correlation between the emergence times of the two males on given nights from the same sett (r = 0-27. df 8; ns). In the winters of 1980-81 and 1981-82 we secured a total of 81 badgernights of data, including 7 instances of stopping. The nightly minimum grass temperatures at the setts varied between - 5.0 °C and 8.0 °C, with a mean of 0.33 °C (SD _ 3.4 °C). The badgers sometimes emerged as early as 20.1 h but on other nights they did not emerge at all. Overall, the time of first emergence in winter differed between the three badgers: for CBF from January to April 1981 it was 02.4h (SD 4.1) including the nights when she never emerged, but 22'4 h on those nights when she did emerge. In November 1982, for SS(A)F and for SSM, on those nights when they did emerge it was 00.4 h (SD 1.8) and 22.1 h (SD 1.5) respectively ( t < 3 . 8 , df 6, p < 0 . 0 1 ) . There was no significant correlation between the emergence times on given nights of SSM and SS(A)F (r = 0-45, df 8; p < 0.2). The most complete data, 57 nights for CBF, are summarised in Table 3. Overall, this sow first became active just after midnight, with her first bout of activity (3 consecutive 5 min sessions) 1.3 h later. The total duration of emergence on those nights when she emerged at all varied from 0.1 to 0.9 h and averaged only 0.29 h (17 min, see Table 3). Figure 3 summarises the data for CBF, SSM and SS(A)F, the three badgers for which there are most data. We measured three variables
TABLE
3
(a) Overall mean (b) Mean (--stopping) (c) Mean stopping only Temperature (Pearson corr. coeff.) Significance 0.33 (3.44) 0-48 (3.49) - 1.2
Temp. (°C)
00.86 (4.16) 00.37 (4-02) 06.00 - 0.63 0-001
0'001
First activity (time)
02.40 (4.10) 02.06 (4.13) 06.00 - 0.82
First emergence (time)
0"001
02.18 (4.15) 01.81 (4.17) 06.00 - 0.73
First burst (time)
0"001
0.20 (0.27) 0-22 (0.27) 0-0 0.58
Duration first emergence (h)
0-001
0.25 0.29 (0.45) 0.0 0.70
Total duration of emergence (h)
5 52
57 52
The Mean Values, with Standard Deviations in Parentheses, of Various Activities of a Badger (CBF) from January to April 1981, (a) Throughout the Study Period, (b) Excluding Stopping Days and (c) for the Nights Following Stopping Days. (The value of a Pearson correlation coefficient, and its significance, is given for the relationship between minimum nightly temperature, measured at the sett, and each of the values excluding stopping (i.e. those from row (b)). Time is expressed as hour (on a 24 h clock) and decimalised minutes.)
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Fig. 3. Plots of the minimum nightly grass temperatures versus times of first emergence from their setts from three badgers, (a) CBF from January to April 1981, (b) SSM in November 1982, and (c) SS(A)F in November 1982. Nights when the badgers did not emerge at all are shown as emergence at 06.00 h. Nights following stopping are shown by open circles. Numbers beside some points indicate the numbers of nights falling on that point. Linear regressions, excluding nights following stopping, are: ( a ) C B F : r - - - 0 . 8 , df 50, p < 0-001 ; (b) SSM: r = - 0 . 9 0 , df 8, p < 0.001 : (c) SS(A)F: r = - 0 . 9 , df 9, p < 0.001. If nights on which the badger did not emerge at all are excluded then: (a) C B F : r = - 0 . 5 6 , df 25, p < 0.01: (b) SSM: r = - 0 . 9 8 , df 5, p < 0.001 ; (c) SS(A)F: r = - 0 . 7 5 , df 5, p < 0-02.
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1. M. Lindsay, D. W~ Macdonald
which might affect emergence time: the minimum temperature, the date, and the incidence of stopping. Figure 3 shows that these badgers did not emerge on any of the seven stopping nights; however, neither did they emerge on 36 (48.6 Vo) of the 74 other nights, when there was no stopping. The mean temperature was low (x = - 0 . 3 °C, range - 5 to + 2, n = 7) on the stopping nights. Therefore, temperature rather than stopping may have prevented the badgers' emergence. Indeed for study nights between January and April, minimum temperature declined with advancing date (r = - 0.2, df 50, p = 0.08). These months of study witnessed a decline in mean monthly minimum temperatures during study nights from 2.1 to - 0 . 1 2 ° C and to - 0 . 3 9 ° C . Coincidentally, the mean time of first emergence was postponed from 01.3 h to 02.5 h to 03.2 h. This coincident decline in mean temperature and postponement of first emergence time may be causally dependent, but both are related to the passage of the seasons. During the January to April (dates labelled 1 to 104) when CBF was studied, emergence time and date were not correlated (r = 0.18, df 50; ns). A regression analysis of time of first emergence and duration of emergence with both date and minimum nightly temperature shows that minimum nightly temperature is much more closely correlated with badger emergence for all study animals. Indeed, for CBF, SSM and SS(A)F date explained little (0 o,,/o,15 ~o, 12 ~,'/o)of the variance in emergence time, whereas minimum nightly temperature explained from 65 ~o, 78 ~o o, and 8A~/o, respectively; in each case minimum nightly temperature correlated negatively with emergence time at p < 0.001. Similarly, for all three badgers, minimum nightly temperature correlated positively (at p < 0.001) with total duration of emergence, and explained 49, 81 and 73 o/ o/ o f the variance. The following equations describe the regressions (p < 0.001 in each case) between emergence parameters and the minimum nightly temperature for CBF: FIRST E M E R G E N C E (time)= 1 4 . 5 6 - 0.98 (rain temp.) (r 2 sq = 0.68) E M E R G E N C E D U R A T I O N (h) -- 0"26 + 0"09 (min temp.) (r 2 sq = 0.49) FIRST ACTIVITY (time) = 12.78 - 0.73 (min temp.) 0"37)
(r 2 sq =
FIRST BURST (time)= 14-34- 0.85 (min temp.) (r 2 sq -- 0.49)
Effects of disturbance on badgers
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These equations and the similar ones for the other badgers indicate that temperature is a close correlate of emergence time. In summary, excluding stopping, on only one of 31 nights when the nightly minimum temperature fell to or below - 1.0 °C did the badgers emerge at all, whereas on all of the 36 nights when the temperature remained above or equal to 1.0 °C they did emerge. Of the 4 nights in our sample when the minimum temperature was 0 °C the badger emerged on two and remained in the sett on the other two. Figure 3 shows the nights tbllowing the seven days on which the setts were stopped. On three of these nights the temperature was below freezing and the badgers did not emerge. The remaining four nights provide the only instances, for three different badgers, when the minimum temperature was above freezing and yet on which the animal did not emerge at all. The expected time of emergence and the duration of emergence, stopping notwithstanding, can both be calculated from the regressions based on the data for these same individuals on Fig. 3. CBF, for example, would have been expected to emerge at 22.3 and 22.4h respectively on the warm nights when her sett was stopped. On these nights the badger lost an estimated 26 and 21 min of emergence, apparently due to stopping. SSM lost the most when he did not emerge on a night with minimum temperature of 2 °C on which he was expected to have spent 37 min out of the sett. DISCUSSION Our data indicate that the emergence of all the study badgers in winter was affected by temperature; they became active and emerged later and remained abroad for less time on colder nights, and never emerged on nights when the minimum grass temperature at the sett fell below freezing. All six badgers were affected in the same way by temperature, and in five cases the effect was highly significant. Doubtless much of the variation in these temperature-emergence time relationships stemmed from the insensitivity of Our single (minimum) measure of nightly temperature. The same lack of information on the time course of nightly temperature changes complicates any speculation on why the badgers should postpone their emergence most on nights when, at some time, the temperature is coldest. Furthermore, the badgers differed in the times at which they emerged on nights of given temperature. In two cases, badgers from the same social group regularly emerged at different times on the same nights.
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Earth stopping by fox hunters was widespread and often directed at badger setts. Regionally, the numbers of badger setts on farmland varied independently of the reported frequency of stopping. Badgers delayed and curtailed their activities on the nights following stopping and, depending on the number of entrances, took several days or longer to reopen most of the blocked holes; many re-opened one hole on the first night after stopping. According to both these measures of disturbances, the magnitude of the effect upon badgers of stopping was dependent upon temperature; holes were re-opened over longer periods when the weather was cold. The method of stopping might also affect the pattern of reopening, but our data concern only stopping with soil. In very cold weather the soil with which the setts' entrances were stopped froze into a solid plug and doubtless this contributed to the delay in re-opening holes. At least for WPF, the delay caused by stopping was least on warm nights. Therefore, according to our measures, earthstopping at setts is amongst the factors affecting badgers' emergence. However, badgers often do not emerge on winter nights, and they may not feed even when they do emerge, but instead they meander in the vicinity of the sett. Possibly their behaviour then has some territorial function. In the context of limited winter emergence and to the extent that our measures are appropriate indices of disturbance, the immediate effects of stopping appear to be slight. We have no evidence that postponement of the short time which badgers spend abroad on warmer winter nights is damaging. Observations at setts in midwinter gave no clue as to the functions of the badgers' activities when they do emerge. This study does not rule out the possibility of a longer term effect upon, say, reproductive success. Nevertheless, stopping of the type described here had been practised in our study area, as elsewhere, for decades, and badgers were still numerous there. In the three years of our study, badger cubs were seen annually at each sett, no sett was abandoned, and radio-tagged badgers which were subjected to stopping never vacated a sett, even temporarily, to move to other holes which were not stopped within their home ranges. Our findings concern setts which were lightly stopped with soil. Unquestionably, stopping with logs, rubble and rocks must cause more disturbance, if only in the sense of requiring major excavations by the badger to unblock or circumvent the stoppage. If badgers were close to an energy threshold in winter, such extra effort could be damaging. However, there is no evidence for this, since badgers in England generally lay down a thick layer of fat in winter. At setts which are habitually
Effects oJ disturbance on badgers
305
heavily stopped with debris the badgers generally excavate new tunnels. Our impression is that the result is an expanding area of spoil heaps, pockmarked by craters left by stopped holes and projecting obstacles; a whole group of entrances may be abandoned, and others excavated adjacent to them. Such departures from M F H A guidelines seem pointless and their consequences undesirable, not least because setts stopped with rubble become an eyesore and those where entrances cover an increasingly large area are more likely to cause a nuisance to farmers. Light stopping with soil appears to have little effect on the winter activity of badgers, but what effect does it have on fox hunting? Doubtless the answer varies regionally with, for example, the population densities of foxes and badgers, and their tendency to cohabit. Of Masters of Foxhounds with whom we corresponded, those from the south and south west of England emphasised that foxes often escaped them by seeking refuge in badger setts and Table 1 shows that the farmers in Cornwall and Sussex recorded rather low levels of stopping. However, for one pack of foxhounds in the English Midlands, we analysed the outcome of all 60 hunting days in the season 1979-80. One-hundred-and-fifteen foxes ran to ground, but only three of these were seen to take refuge in main badger setts. Of course, since there was no control area free of stopping, one cannot evaluate the argument that this low figure is the consequence of stopping badger setts. However, that argument is weakened, but not demolished, by our finding that setts in that area were neither always stopped nor always stopped completely. An alternative hypothesis is that, at least in some regions, places where hunted foxes can go to ground are so numerous that there is a low probability of (a) their seeking refuge in a badger sett in the first place, and (b) their being unable to find an alternative refuge if the sett is stopped. The plausibility of this latter suggestion increases as the labour force of lull-time professional earthstoppers diminishes: thus the effectiveness of earthstopping in keeping foxes above ground may be different now from what it was a century ago.
ACKNOWLEDGEMENTS We gratefully acknowledge Mrs de Rothschild and Mrs Spencer Barnard for allowing us to work on their properties and Captain I. Farquhar, the late Frank Tutt and the M F H A for their cooperation. This .work was
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conducted while D W M was an Ernest Cook Fellow, whereas I M L was sponsored latterly by the People's Trust for Endangered Species; we are grateful to them and to the other sponsors who have supported our longer term badger research. Drs C. Dickman, H. Kruuk and H. Hofer kindly commented on an earlier draft. The badgers were caught under the conditions of a licence issued to D W M by the Nature Conservancy Council, whose cooperation is gratefully acknowledged.
REFERENCES Amlaner, C. J. (1980). The design of antennas for use in radio telemetry. In A handbook on biotelemetry and radio tracking, ed. by C. J. Amlaner and D. W. Macdonald, 251-62. Oxford, Pergamon Press. Kruuk, H. (1978). Spatial organisation and territorial behaviour of the European badger, Meles meles. J. Zool. Lond., 184, 1-19. Macdonald, D. W. (1984). A questionnaire survey of farmers' opinions and actions towards wildlife on farmland. In Agriculture and the environment, ed. by D. Jenkins, 171-7. Cambridge, Institute of Terrestrial Ecology (NERC) Publication. Macdonald, D. W. & Amlaner, C. J. (1980). A practical guide to radio tracking. In A handbook on biotelemetry and radio tracking, ed. by C. J. Amlaner and D. W. Macdonald, 143-60. Oxford, Pergamon Press. Neal, E. (1977a). Badgers. Poole, Blandford Press. Neal, E. (1977b). Badger. In The handbook of British mammals, ed. by G. B. Corbet and H. N. Southern, 357-66. Oxford, Blackwell.
The Effects of Disturbance on the Emergence of Eurasian Badgers in Winter
I. M. Lindsay & D. W. Macdonald Department of Zoology, South Parks Road, Oxford OXI 3PS, Great Britain
ABSTRACT Eurasian badgers are widespread on English farmland where they may be affected by various human activities, amongst which is the practice of 'earthstopping' by foxhunts. This practice is described in detail, and involves blocking the entrances to badger setts in order to prevent the escape therein of hunted foxes. A questionnaire survey indicates that earthstopping is practised on 30.8 % of English fiTrms and that in some areas most badger setts are routinely stopped 4-5 times during the winter foxhunting season. Setts were monitored and badgers radio-tracked in an investigation of the consequences of stopping for their behaviour. The time of nightly emergence from the sett was found to be negatively correlated with minimum nightly temperature, and badgers rarely emerged at all on nights when the temperature fell to - 1 °C or below. When subjected to stopping the badgers postponed their emergence times and did not emerge at all on some nights when, on the basis of the temperature, they would otherwise have been expected to do so. However, we could detect no damaging effect upon the badgers due to these delays or otherwise due to stopping when it was practised responsibly. In contrast, irresponsible stopping with rubble rather than loose soil is pointless, damaging to the landscape andprobably also to the badgers. We conclude that where stopping is deemed necessary it should only be done either with loose soil, which the badgers can readily dislodge, or with bungs such as soil-filled sacks, which the huntsmen should remove at the end of the day's hunting. 289 Biol. Conserv. 0006-3207/85/$03.30 ~/Elsevier Applied Science Publishers Ltd. England 1985. Printed in Great Britain
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I N T R O D U C T I ON The Eurasian badger, Meles meles, is a 10kg nocturnal mustelid (subfamily Melinae) which lives in territorial groups of 2-12 members, that occupy a communal den or sett (Neal, 1977a: Kruuk, 1978). In addition to the 'main sett7 which is often located centrally in the territory, there are other holes, termed 'outliers', which some badgers may use intermittently. Main setts comprise several entrances (generally 6-10 but 100 have been recorded, Neal, 1977a) and are in traditional sites which may have been used continuously for centuries. In mid-winter, badgers remain largely in the sett. This period of inactivity may last, in Great Britain, from December to March. Eurasian badgers in Britain are widespread on farmland (Neal, 1977b) where they are tolerated, and even welcomed, by most farmers, to whom they generally cause minimal damage (Macdonald, 1984). On about 80 ~/oof English farmland red foxes Vulpes vulpes are hunted with hounds and mounted followers. When pursued, foxes may seek sanctuary underground, including badgers' setts, in which they often shelter by day even when undisturbed. Therefore, burrows in general, and badger setts in particular, are seen as an impediment to fox hunting for two reasons: first, a hunted fox taking refuge in a burrow may thereby escape completely, or necessitate laborious and protracted digging-out. Either outcome diminishes the opportunities for challenging horsemanship for the assembled 'field'. Second, loxes which have taken refuge in holes before the hunt arrives are from the outset much less accessible. In an attempt to avert these problems, fox hunters block burrow entrances into which foxes might flee or lie-up--a practice known as ~earthstopping'. During the foxhunting season (September to March) the entrances to badger setts are ~stopped' on hunting days throughout much of rural England. Setts are also sometimes stopped by farmers or others who are not necessarily concerned with hunting. The practice of stopping setts is controversial in that it might have damaging consequences for the badgers. In the hope of diminishing any such consequences the fox hunters" governing body (Masters of Foxhounds Association, MFHA) issues guidelines for earthstoppers; they recommend that sett entrances may be blocked with loose balls of wire mesh which can easily be removed by hunt servants and which allow the passage of air. Alternatively, they suggest that sacks filled with soil can be used as temporary bungs to be removed at the end of the day (e.g. in the
Effects of disturbance on badgers
291
pamphlet Predator), mammals in Britain, Council for Nature, 1977). However, there are no data on the consequences tbr badgers of stopping, or how closely the guidelines are followed. Various potentially deleterious effects of stopping have been mooted, including prevention or delay of emergence, stress-induced reproductive failure and desertion of the sett, suffocation, and unsustainable expenditure of energy to unblock holes at a time when food is scarce. Within the context of a wider study of the ecology of badgers on farmland in the English Midlands we have sought to quantify the types of disturbance to which they are subjected. Disturbance due to agricultural activities appears generally to be infrequent and tolerable, and is summarised elsewhere (Macdonald, 1984). In this paper we will describe and quantify earthstopping on farmland and some of its consequences. In particular, by studying its effects on their emergence times, we will try to answer the question of whether earthstopping is detrimental to badgers. A change due to earthstopping in the time of emergence from the sett has the merit of being an immediate and readily quantifiable measure of disturbance. In selecting this measure we recognised that it does not reveal some of the possible long-term consequences, for example, changes in reproductive success, but measurement of these were beyond the scope of our study. We have, however, monitored sett utilisation throughout the study, in order to assess whether stopping was associated with any change in the pattern of occupation.
METHODS
Frequency and distribution of stopping Two questionnaires were sent to farmers, each enquiring about diverse aspects of wildlife on their farms. Respondents to the first questionnaire (Sample A, 1979 80) numbered 867 and came from 10 regions of England, whereas the 101 respondents to the second questionnaire (Sample B, 1982) came from Buckinghamshire, Oxfordshire and Warwickshire. Farmers in Sample A were asked 'How many badger setts do you know of on your land ?' and "Are fox and badger holes stopped on hunting days?'. Farmers in Sample B were also asked about numbers of setts on their land and, specifically, whether badger setts were stopped on hunting days. In enquiring about badger setts we told farmers that 'Setts
292
I.M. Lindsay, D. W. Macdonald
can be recognised as a clump of 2 or more entrance holes (each about 10" diameter) with large spoil heaps of soil. Setts are normally occupied for many years. Individual badgers may occasionally live in single holes 100 yds or more from the main sett, but we do not count these "outliers" as "main setts". Please confine your answers to main setts'. We were aware of the difficulties of defining main setts and of relating numbers of setts to numbers of social groups, but felt that these guidelines were easy to comprehend and adequate to define most main setts (cf descriptions in Neal, 1977a).
Stopping of badger setts and re-opening Our field study area, like most of rural England, fell within the 'country' (territory) of one pack of foxhounds. By daily visits to a sample of main setts we recorded the incidence and details of stopping. After a day of fox hunting we then monitored the badgers' activities in re-opening blocked entrances over subsequent days.
Factors affecting emergence In our study area, 30km 2 around the village of Waddesdon, Buckinghamshire, badgers were equipped with 102 KHz radio transmitters fitted to leather collars. The transmitters followed the two-stage circuitry designed by Macdonald & Amlaner (1980) and were equipped with a motion-sensitive mercury switch. Signals were received on a Telemetry Systems Inc. (Minneapolis, USA), receiver, via either a threeelement Yagi antenna mounted on a car or via a collapsible dipole antenna, used on foot (for construction details see Amlaner, 1980). Observations at setts confirmed that a combination of changes in signal strength and activity (indicated by the motion-sensitive switch) heralded the emergence of a radio-tagged badger from its sett. In this study of the consequences of 'stopping' we were concerned with emergence in winter, when badgers sometimes leave the sett only late at night or not at all (Neal, 1977a). Observation at setts was thus hopelessly unrewarding and so we utilised an automatic timing box and recorder to monitor the radiosignals all night. The apparatus is described in Macdonald & Almaner (1980). The timing box scanned the required radio-frequencies and recorded the signal from each for 10 s every 5 rain. Listening to the tape we
Effects of disturbance on badgers
293
scored the volume of the signal on a subjective scale of increasing volume (1-5) and whether the mercury switch indicated movement. Comparing these 10 s transcriptions with the signal characteristics of badgers under observation, we decided the times at which badgers emerged from or returned to their setts. For some individuals we also scored the times at which they first became active each night and the first burst of protracted activity, as indicated by three consecutive active scans (i.e. spanning 10min). Times will be given in hours and decimal minutes. Where calculations involve nights on which a badger failed to emerge at all these are scored as emergence at 06.00 h in the morning (all such calculations use a 24h clock running from midday, so that 06.00 h is taken as 18.00 h during the calculation). In general, emergence from the sett was quite easily recognised by increased activity together with a change from a muffled to a sharp signal tone and a marked increase in signal volume. Sometimes, however, interpretation was ambiguous. For example, a similar record could result from a badger either poking its head from a hole and then retreating underground, and from another which emerged and then rapidly left the area. Of our various measures, duration of emergence was most susceptible to this type of ambiguity, but time of first emergence from the sett was generally clearcut. Ambiguity of this type was minimal largely because the badgers rarely left the vicinity (c. 50-100m) of the sett when they emerged. Transcriptions were least confusing the more continuous the night's record;we found that the 5 min interval and 10 s scan was the best compromise, minimising ambiguity and redundancy, while neither exceeding the capacity of the tape spool nor generating an insurmountable task in transcription. It will be shown that badgers differ individually in their emergence behaviour. Therefore, we have compared the activity of the same individuals when they are, or are not, subjected to stopping, while taking into account other possible relevant factors. Individual badgers will be referred to by the two letter code of their sett and a third letter (M or F) denoting their sex; thus CBF is a sow from sett CB. In one case the radiocollared badger SS(A)F lived in an annex about 100 m from the main sett. On each night when a badger's activity was monitored, the weather conditions were also noted and a record taken of the night's minimum ground temperature, using a maximum and minimum thermometer. The incidence of stopping was monitored at setts where badgers were radiocollared. At these setts all entrances were stopped, using soil, and none was reopened by people.
294
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RESULTS
Frequency and disturbance Of the 867 farmers who responded in Sample A, 604 answered the question of whether or not holes (badger or other) on their land were stopped on hunting days. 30.8 ~ replied that fox and badger holes were stopped on their land. Their answers are presented regionally in Table 1. The regional differences in frequency of stopping do not correlate with the number of setts reported per km sq estimated from the same farmers' reports on the number of badger setts on their land (r = - 0 . 2 , df. 8; ns). Table 1 also shows the regional variation in the percentage of farmers who at least occasionally follow foxhounds, and this figure does correlate weakly with the frequency of stopping (r = 0.57, df. 8; p < 0.1 > 0.05). The answers from respondents in Sample B gave a similar impression; 45 of the 101 farms reported the presence of main setts, and on 29 (64.4 ~o) of these the setts were stopped on hunting days (modally 4-5 times per season). Overall, foxes were hunted with hounds on 82.2 ~ of these 101 farms, and open holes (badger or other) were stopped on hunting days on 29 ~ . The only farmers who reported stopping on their land were those who reported badger setts, suggesting that hunt servants concentrate their stopping activities on badger, rather than fox, holes. Extrapolating from these figures one can see that earthstopping affects a large number of badgers. For example, in the English Midlands, from which our sample farms were drawn, farmers reported a mean of 0.5 setts per km 2 of farmland, equivalent to one sett stopped per 3.1 km 2 of farmland. In fact, in the 700 km 2 covered by the foxhunt in our study area, figures provided by hunt servants suggested that roughly 200 setts were routinely stopped during the foxhunting season.
Stopping and re-opening In summer, the 27 setts in our core study area had an average of 9.8 unobstructed entrances (SD 4.5), with most (53-6~) having 6-10 entrances. An earthstopper arriving at a sett attempts to find and block every entrance. The prevalent method of stopping with soil simply involved shovelling soil into the entrance and stamping it firmly into place. Holes that had been stopped are often recognisable by angular rather than circular entrances due to old spade cuts. In our area neither
TABLE 1
o~ 'Stopping' /o N Badger setts (km -2) ~o Foxhunters
30.8 604 1-2 33.9
28,3 99 0.5 30.4
Overall Ox/Bucks 21-0 62 1.1 30-5
Warks 57.9 107 2.5 40.5
Dorset 39.7 31 0.3 22,4
Salop 40"9 44 0.3 38"0
Leics 15-5 77 0-2 38.2
Yorks
5'0 20 2.3 22.5
12.5 24 0.1 18.4
Cornwall Suffolk
45-6 57 1'4 62.8
Exmoor
8"9 67 2.5 26-8
Sussex
The Overall and Regional Percentage of Farmers in Sample A Who Reported that Either Badger or Fox Holes were Stopped on Their Land on Stopping Days, Together with the Density of Badger Setts per km sq and the Percentage of Farmers who Stated that they at Least Occasionally Engaged in Foxhunting (The density of badger setts was calculated from each farmer's estimate of the number oflsetts on his land and the farm's area. The numbers of farmers answering each question on the questionnaire varied slightly and the sample sizes given here (N) refer to those answering the question on stopping, which represents 69.7 ~ of the total sample of respondents. The estimates of sett density and the percentage of hunting farmers are based on the answers of 676 and 853 respondents, respectively.)
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296
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plugs of wire nor of soil-filled sacks were used. Sometimes empty fertiliser bags, logs, metal drums and other rubble or debris were used in an attempt to block entrances permanently, when they might also be stuffed with diesel-soaked rags. Pock-marks in the ground around setts may indicate that some holes are never re-opened. We visited 30 setts during the days following their being stopped for hunting. Only 80 ~ of the entrances had, on average, been re-opened after two weeks. During the first night between 10-100 ~o of stopped holes are unblocked by badgers (holes re-opened by rabbits, and hence with a diameter too narrow for badgers to pass, were excluded). On average the badgers opened 2.4 (SD + 1.4, n = 39) holes on the first night after stopping, and a steadily increasing percentage of holes had been re-opened as days passed (r = 0.37, df 166, p < 0.001). Some holes might remain blocked for three weeks or more, and the rate of re-opening was affected by the total number of entrances at the sett. Thus, at small ( < 4 entrances) setts a mean of 1.2 (SD + 0.4, n = 11) holes were re-opened on the first night, while at larger ones (> 4 entrances) this mean was 2.9 (SD + 1.3, n = 26). A multiple regression of percentage of entrances re-opened against days (up to 21) since stopping and number of sett entrances gave a multiple regression coefficient of 0.55 (df 166, p < 0.001) with the two independent variables accounting for 13 ~ and 18 ~o of the variance respectively. A partial correlation analysis controlling for sett size alone (r = 0.4, df 165, p <0.001) is not improved by additionally controlling for month (advancing from September to February). In summary, up to six holes might be re-opened on the first night, a greater percentage remaining unopened at larger setts on subsequent days. This pattern is shown in Fig. 1, which presents the mean percentages of re-opened holes, for setts of different sizes, on successive days after stopping. The slopes for regressions through these means intersect with the first night at 51.1 ~ , 41.2 ~ and 17.2 ~o of holes re-opened at small, medium and large setts respectively. A comparison of the number of open entrances seen at each sett at the beginning and the end of the hunting season for 16 setts which were stopped showed a decline during each of two years; in 1978 to 1979 the mean number of open entrances fell from 8.4 to 6.6 (a mean percentage change of - 2 9 . 4 ~) during the hunting season, whereas in 1979-80 it fell from 7.2 to 6.4 (a mean percentage change of - 10-I ~o), by 10.1 ~ , for the same setts. During 1978-79 three setts maintained their initial complement of entrances by the end of the season, while in 1979-80 eight
Effects of disturbance on badgers
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Emergence studies Over three years the emergence activities of seven radio-collared badgers from 5 setts were monitored using the automatic timing box. The results
I . M . Lindsay, D. W. Macdonald
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for 1979-80 are presented separately from those for 1980-81 and 1981-82, since in the first season data on temperature were measured at a nearby airforce base, and not at the setts themselves. One badger, WPM, studied in January and February 1980, only emerged twice in 21 nights and therefore could not be used in the following analyses. All six of the remaining badgers yield a negative slope relating time of first emergence to minimum nightly grass temperature, and for five of them this relationship was significant at p < 0.01. Despite this overall relationship, the badgers differed in their behaviour, as detailed below. Between January and March 1980 time of first emergence was recorded for W P F on 22 nights, including 9 when the sett had been stopped. On the latter 9 nights the mean emergence time of the badger was 00.70h, whereas on the remaining 13 undisturbed nights it was 21.50 h. Overall, therefore, a delay of 3.2 h (3 h 12 min) was associated with stopping, but as shown on Table 2, this delay was influenced also by temperature; On warm nights (min > 5.0 °C) the mean delay was 1 h 14 min. The only night on which the badger did not emerge at all followed stopping, when the minimum temperature was rather high at 2.0°C. Two males from the same sett, WIM! and WIM2, monitored for 14 nights during November and December 1979, both emerged later, on average, than W P F (t _< 5.3, df 25, p < 0.001). Although both these males had the same mean
299
Effects of disturbance on badgers
TABLE 2 Variation in the Mean Time of First Emergence from the Sett of One Badger (WPF) from January to March 1980, Contrasting Nights when Setts Had, or Had Not, Been Stopped During the Previous Day (The badger emerged later following stopping and this delay is shown for cold, mild and warm nights (nightly mean temperatures measured at a nearby meteorological station). Time is expressed as hour (on a 24 h clock) and decimalised minutes.) Min. temp. °C
>5.0 <5.0>2.0 <2.0
No stopping
Stopping
Mean Mean Ist rain. °C emergence
n
6.5 3.6 -0.7
7 5 3
20.6 22.2 22.4
Delay
Mean Mean Ist rain °C emergence
5.0 3.7 1.3
21.8 1.7 2.6
3 3 3
1.2 3.5 4.2
emergence time on those nights when they did emerge (23.00h versus 23.43 h), WIM2 emerged significantly later on colder nights (r = - 0 . 7 2 , df 12; p < 0-01) whereas WIM1 did not (r = - 0 . 3 , df 11 ; ns). Thus there was no correlation between the emergence times of the two males on given nights from the same sett (r = 0-27. df 8; ns). In the winters of 1980-81 and 1981-82 we secured a total of 81 badgernights of data, including 7 instances of stopping. The nightly minimum grass temperatures at the setts varied between - 5.0 °C and 8.0 °C, with a mean of 0.33 °C (SD _ 3.4 °C). The badgers sometimes emerged as early as 20.1 h but on other nights they did not emerge at all. Overall, the time of first emergence in winter differed between the three badgers: for CBF from January to April 1981 it was 02.4h (SD 4.1) including the nights when she never emerged, but 22'4 h on those nights when she did emerge. In November 1982, for SS(A)F and for SSM, on those nights when they did emerge it was 00.4 h (SD 1.8) and 22.1 h (SD 1.5) respectively ( t < 3 . 8 , df 6, p < 0 . 0 1 ) . There was no significant correlation between the emergence times on given nights of SSM and SS(A)F (r = 0-45, df 8; p < 0.2). The most complete data, 57 nights for CBF, are summarised in Table 3. Overall, this sow first became active just after midnight, with her first bout of activity (3 consecutive 5 min sessions) 1.3 h later. The total duration of emergence on those nights when she emerged at all varied from 0.1 to 0.9 h and averaged only 0.29 h (17 min, see Table 3). Figure 3 summarises the data for CBF, SSM and SS(A)F, the three badgers for which there are most data. We measured three variables
TABLE
3
(a) Overall mean (b) Mean (--stopping) (c) Mean stopping only Temperature (Pearson corr. coeff.) Significance 0.33 (3.44) 0-48 (3.49) - 1.2
Temp. (°C)
00.86 (4.16) 00.37 (4-02) 06.00 - 0.63 0-001
0'001
First activity (time)
02.40 (4.10) 02.06 (4.13) 06.00 - 0.82
First emergence (time)
0"001
02.18 (4.15) 01.81 (4.17) 06.00 - 0.73
First burst (time)
0"001
0.20 (0.27) 0-22 (0.27) 0-0 0.58
Duration first emergence (h)
0-001
0.25 0.29 (0.45) 0.0 0.70
Total duration of emergence (h)
5 52
57 52
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Fig. 3. Plots of the minimum nightly grass temperatures versus times of first emergence from their setts from three badgers, (a) CBF from January to April 1981, (b) SSM in November 1982, and (c) SS(A)F in November 1982. Nights when the badgers did not emerge at all are shown as emergence at 06.00 h. Nights following stopping are shown by open circles. Numbers beside some points indicate the numbers of nights falling on that point. Linear regressions, excluding nights following stopping, are: ( a ) C B F : r - - - 0 . 8 , df 50, p < 0-001 ; (b) SSM: r = - 0 . 9 0 , df 8, p < 0.001 : (c) SS(A)F: r = - 0 . 9 , df 9, p < 0.001. If nights on which the badger did not emerge at all are excluded then: (a) C B F : r = - 0 . 5 6 , df 25, p < 0.01: (b) SSM: r = - 0 . 9 8 , df 5, p < 0.001 ; (c) SS(A)F: r = - 0 . 7 5 , df 5, p < 0-02.
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which might affect emergence time: the minimum temperature, the date, and the incidence of stopping. Figure 3 shows that these badgers did not emerge on any of the seven stopping nights; however, neither did they emerge on 36 (48.6 Vo) of the 74 other nights, when there was no stopping. The mean temperature was low (x = - 0 . 3 °C, range - 5 to + 2, n = 7) on the stopping nights. Therefore, temperature rather than stopping may have prevented the badgers' emergence. Indeed for study nights between January and April, minimum temperature declined with advancing date (r = - 0.2, df 50, p = 0.08). These months of study witnessed a decline in mean monthly minimum temperatures during study nights from 2.1 to - 0 . 1 2 ° C and to - 0 . 3 9 ° C . Coincidentally, the mean time of first emergence was postponed from 01.3 h to 02.5 h to 03.2 h. This coincident decline in mean temperature and postponement of first emergence time may be causally dependent, but both are related to the passage of the seasons. During the January to April (dates labelled 1 to 104) when CBF was studied, emergence time and date were not correlated (r = 0.18, df 50; ns). A regression analysis of time of first emergence and duration of emergence with both date and minimum nightly temperature shows that minimum nightly temperature is much more closely correlated with badger emergence for all study animals. Indeed, for CBF, SSM and SS(A)F date explained little (0 o,,/o,15 ~o, 12 ~,'/o)of the variance in emergence time, whereas minimum nightly temperature explained from 65 ~o, 78 ~o o, and 8A~/o, respectively; in each case minimum nightly temperature correlated negatively with emergence time at p < 0.001. Similarly, for all three badgers, minimum nightly temperature correlated positively (at p < 0.001) with total duration of emergence, and explained 49, 81 and 73 o/ o/ o f the variance. The following equations describe the regressions (p < 0.001 in each case) between emergence parameters and the minimum nightly temperature for CBF: FIRST E M E R G E N C E (time)= 1 4 . 5 6 - 0.98 (rain temp.) (r 2 sq = 0.68) E M E R G E N C E D U R A T I O N (h) -- 0"26 + 0"09 (min temp.) (r 2 sq = 0.49) FIRST ACTIVITY (time) = 12.78 - 0.73 (min temp.) 0"37)
(r 2 sq =
FIRST BURST (time)= 14-34- 0.85 (min temp.) (r 2 sq -- 0.49)
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These equations and the similar ones for the other badgers indicate that temperature is a close correlate of emergence time. In summary, excluding stopping, on only one of 31 nights when the nightly minimum temperature fell to or below - 1.0 °C did the badgers emerge at all, whereas on all of the 36 nights when the temperature remained above or equal to 1.0 °C they did emerge. Of the 4 nights in our sample when the minimum temperature was 0 °C the badger emerged on two and remained in the sett on the other two. Figure 3 shows the nights tbllowing the seven days on which the setts were stopped. On three of these nights the temperature was below freezing and the badgers did not emerge. The remaining four nights provide the only instances, for three different badgers, when the minimum temperature was above freezing and yet on which the animal did not emerge at all. The expected time of emergence and the duration of emergence, stopping notwithstanding, can both be calculated from the regressions based on the data for these same individuals on Fig. 3. CBF, for example, would have been expected to emerge at 22.3 and 22.4h respectively on the warm nights when her sett was stopped. On these nights the badger lost an estimated 26 and 21 min of emergence, apparently due to stopping. SSM lost the most when he did not emerge on a night with minimum temperature of 2 °C on which he was expected to have spent 37 min out of the sett. DISCUSSION Our data indicate that the emergence of all the study badgers in winter was affected by temperature; they became active and emerged later and remained abroad for less time on colder nights, and never emerged on nights when the minimum grass temperature at the sett fell below freezing. All six badgers were affected in the same way by temperature, and in five cases the effect was highly significant. Doubtless much of the variation in these temperature-emergence time relationships stemmed from the insensitivity of Our single (minimum) measure of nightly temperature. The same lack of information on the time course of nightly temperature changes complicates any speculation on why the badgers should postpone their emergence most on nights when, at some time, the temperature is coldest. Furthermore, the badgers differed in the times at which they emerged on nights of given temperature. In two cases, badgers from the same social group regularly emerged at different times on the same nights.
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Earth stopping by fox hunters was widespread and often directed at badger setts. Regionally, the numbers of badger setts on farmland varied independently of the reported frequency of stopping. Badgers delayed and curtailed their activities on the nights following stopping and, depending on the number of entrances, took several days or longer to reopen most of the blocked holes; many re-opened one hole on the first night after stopping. According to both these measures of disturbances, the magnitude of the effect upon badgers of stopping was dependent upon temperature; holes were re-opened over longer periods when the weather was cold. The method of stopping might also affect the pattern of reopening, but our data concern only stopping with soil. In very cold weather the soil with which the setts' entrances were stopped froze into a solid plug and doubtless this contributed to the delay in re-opening holes. At least for WPF, the delay caused by stopping was least on warm nights. Therefore, according to our measures, earthstopping at setts is amongst the factors affecting badgers' emergence. However, badgers often do not emerge on winter nights, and they may not feed even when they do emerge, but instead they meander in the vicinity of the sett. Possibly their behaviour then has some territorial function. In the context of limited winter emergence and to the extent that our measures are appropriate indices of disturbance, the immediate effects of stopping appear to be slight. We have no evidence that postponement of the short time which badgers spend abroad on warmer winter nights is damaging. Observations at setts in midwinter gave no clue as to the functions of the badgers' activities when they do emerge. This study does not rule out the possibility of a longer term effect upon, say, reproductive success. Nevertheless, stopping of the type described here had been practised in our study area, as elsewhere, for decades, and badgers were still numerous there. In the three years of our study, badger cubs were seen annually at each sett, no sett was abandoned, and radio-tagged badgers which were subjected to stopping never vacated a sett, even temporarily, to move to other holes which were not stopped within their home ranges. Our findings concern setts which were lightly stopped with soil. Unquestionably, stopping with logs, rubble and rocks must cause more disturbance, if only in the sense of requiring major excavations by the badger to unblock or circumvent the stoppage. If badgers were close to an energy threshold in winter, such extra effort could be damaging. However, there is no evidence for this, since badgers in England generally lay down a thick layer of fat in winter. At setts which are habitually
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heavily stopped with debris the badgers generally excavate new tunnels. Our impression is that the result is an expanding area of spoil heaps, pockmarked by craters left by stopped holes and projecting obstacles; a whole group of entrances may be abandoned, and others excavated adjacent to them. Such departures from M F H A guidelines seem pointless and their consequences undesirable, not least because setts stopped with rubble become an eyesore and those where entrances cover an increasingly large area are more likely to cause a nuisance to farmers. Light stopping with soil appears to have little effect on the winter activity of badgers, but what effect does it have on fox hunting? Doubtless the answer varies regionally with, for example, the population densities of foxes and badgers, and their tendency to cohabit. Of Masters of Foxhounds with whom we corresponded, those from the south and south west of England emphasised that foxes often escaped them by seeking refuge in badger setts and Table 1 shows that the farmers in Cornwall and Sussex recorded rather low levels of stopping. However, for one pack of foxhounds in the English Midlands, we analysed the outcome of all 60 hunting days in the season 1979-80. One-hundred-and-fifteen foxes ran to ground, but only three of these were seen to take refuge in main badger setts. Of course, since there was no control area free of stopping, one cannot evaluate the argument that this low figure is the consequence of stopping badger setts. However, that argument is weakened, but not demolished, by our finding that setts in that area were neither always stopped nor always stopped completely. An alternative hypothesis is that, at least in some regions, places where hunted foxes can go to ground are so numerous that there is a low probability of (a) their seeking refuge in a badger sett in the first place, and (b) their being unable to find an alternative refuge if the sett is stopped. The plausibility of this latter suggestion increases as the labour force of lull-time professional earthstoppers diminishes: thus the effectiveness of earthstopping in keeping foxes above ground may be different now from what it was a century ago.
ACKNOWLEDGEMENTS We gratefully acknowledge Mrs de Rothschild and Mrs Spencer Barnard for allowing us to work on their properties and Captain I. Farquhar, the late Frank Tutt and the M F H A for their cooperation. This .work was
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conducted while D W M was an Ernest Cook Fellow, whereas I M L was sponsored latterly by the People's Trust for Endangered Species; we are grateful to them and to the other sponsors who have supported our longer term badger research. Drs C. Dickman, H. Kruuk and H. Hofer kindly commented on an earlier draft. The badgers were caught under the conditions of a licence issued to D W M by the Nature Conservancy Council, whose cooperation is gratefully acknowledged.
REFERENCES Amlaner, C. J. (1980). The design of antennas for use in radio telemetry. In A handbook on biotelemetry and radio tracking, ed. by C. J. Amlaner and D. W. Macdonald, 251-62. Oxford, Pergamon Press. Kruuk, H. (1978). Spatial organisation and territorial behaviour of the European badger, Meles meles. J. Zool. Lond., 184, 1-19. Macdonald, D. W. (1984). A questionnaire survey of farmers' opinions and actions towards wildlife on farmland. In Agriculture and the environment, ed. by D. Jenkins, 171-7. Cambridge, Institute of Terrestrial Ecology (NERC) Publication. Macdonald, D. W. & Amlaner, C. J. (1980). A practical guide to radio tracking. In A handbook on biotelemetry and radio tracking, ed. by C. J. Amlaner and D. W. Macdonald, 143-60. Oxford, Pergamon Press. Neal, E. (1977a). Badgers. Poole, Blandford Press. Neal, E. (1977b). Badger. In The handbook of British mammals, ed. by G. B. Corbet and H. N. Southern, 357-66. Oxford, Blackwell.